1. Field of the Invention
The invention relates to a telephone device, and in particular to a telephone device for preventing a long-term on-line state resulting from the telephone's handset being unintentionally off-hook.
2. Description of the Prior Art
Referring to FIG. 1, the basic structure of a telephone according to the prior art is shown. The depicted telephone is of the type which generates Dual Tone Multi-Frequency (DTMF) sounds for the purpose of dialing telephone calls. The telephone according to the prior art comprises: a telephone line interface circuit 10 serving as an interface between a ring line and a tip line, and an internal circuit, wherein a switch hook controls the off-hook/on-hook states of the telephone; a ring detector 12 for sensing a ringing signal; a hybrid circuit 16 dividing connecting ends of the telephone line interface circuit into an input end and output end; a dual-tone multi-frequency generator 18 (i.e., a dialing IC) generating a dual-tone multi-frequency signal; a push-button pad 22 outputting a control signal or numeral signal to the dual-tone multi-frequency generator 18; a switch 24 controlled by the dual-tone multi-frequency generator 18, wherein a sound signal from a handset is interrupted as soon as the dual-tone multi-frequency generator 18 outputs a dual-tone multi-frequency signal; and a handset 26 including a receiver (for example, an earphone) and a transmitter (for example, a microphone) for receiving and transmitting the sound signal.
Generally, the off-hook/on-hook states of the above-mentioned telephone are determined by the position of the handset. As is well known, the telephone must be in an on-hook state if it is to receive incoming telephone calls. If it is off-hook, then the telephone can not be connected to from the outside, regardless of whether it is in use or not. Particularly, the handset is inadvertently placed in the off-hook position, a long-term off-hook state results. As a result, the user will not discover this situation until the user needs to use the telephone or an alarm signal from the telephone company switch is transmitted to the telephone to generate a sound signal of higher frequency and amplitude in order to inform the user of the unconnected off-hook state.